70 MONTROSE T. BURROWS 



when degeneration was noticed. Death may be very sudden, in- 

 volving all the cells in a short period of time. In carefully handled 

 specimens, however, the first signs of degeneration were near the 

 tissue originally tiansplanted. The more distant cells died at a 

 considerably later period. 



The rhythm of the heart continues normal in the plasma unless 

 it is disturbed by adhesions to the clot. As a general rule, the 

 cut ends of this organ immediately become attached to the fibrin, 

 first by adhesion, later by the extension outward of a large number 

 of spindle-shaped mensenchyme cells. The rest of the organ, 

 unless injured, gradually frees itself fiom its loose fibrin attach- 

 ments through its constant activity and beats in an open serum 

 cavity. These hearts beat for the first three days with a normal 

 rhythm. After the third, the rhythm and the force of the heart 

 are periodically altered. There is a gradual slowing of activity 

 accompanied by alternate periods of acceleration and inactivity. 

 The activity ceases completely between the third and the eighth 

 day.^ 



The neural tube at the time of tiansplantation, as seen in prep- 

 arations stained in toto and in serial sections, lies firmly held in a 

 fine granular fibrin net. The fibrin lies for the most part without 

 the tube. The central canal is filled with serum. The nerve cells 

 are in their normal relations and react normally to stains. About 

 the outside and closely adherent to th? neural tube is a thin layer 

 of mesenchyme cells not removed at operation. This layer of 

 mesenchyme is veij' thin, generally one or two cells thick, and 

 rarely continuous over the entire tube. 



Examinations of a whole transplanted neural tube shows in 

 gross after the third or fourth day a wide layer of cells growing 

 in plasma about a well formed tube. In serial sections, the nerve 

 cells are seen to be undergoing degeneration. The central canal is 

 filled with dead cells and debris. The outer layer of mesenchyme 

 cells, on the other hand, has developed into a layer many cells 



1 Hooker has shown that the heart functions and develops normally in frog^ 

 embryos after the nervous system had been entirely removed at a period before 

 any nerve fibres had developed. If nourishment were renewed sufficiently often 

 to these isolated hearts, function and development would undoubtedly proceed 

 for a long period of time. 



